Systems and methods for forming elongated lesion patterns in body tissue using straight or curvilinear electrode elements

ABSTRACT

Systems and associated methods position arrays of multiple emitters of ablating energy in straight or curvilinear positions in contact with tissue to form elongated lesion patterns. The elongated lesion patterns can continuous or interrupted, depending upon the orientation of the energy emitters.

This is a continuation Ser. No. 08/287,192 filed Aug. 8, 1994 nowabandoned; which is a continuation-in-part of application Ser. No.08/138,142 filed Oct. 15, 1993 now abandoned; and a continuation in partof application Ser. No. 08/136,680 filed Oct. 13, 1993 now abandoned;and continuation-in-part of application Ser. No. 08/137,576 filed Oct.15, 1993 now abandoned; and a continuation-in-part of application Ser.No. 08/138,235 filed Oct. 15, 1993 now abandoned and acontinuation-in-part of application Ser. No. 08/138,452 filed Oct. 14,1993 now abandoned.

FIELD OF THE INVENTION

The invention relates to systems and methods for ablating myocardialtissue for the treatment of cardiac conditions.

BACKGROUND OF THE INVENTION

Physicians make use of catheters today in medical procedures to gainaccess into interior regions of the body to ablate targeted tissueareas. It is important for the physician to be able to precisely locatethe catheter and control its emission of energy within the body duringtissue ablation procedures.

For example, in electrophysiological therapy, ablation is used to treatcardiac rhythm disturbances.

During these procedures, a physician steers a catheter through a mainvein or artery into the interior region of the heart that is to betreated. The physician places an ablating element carried on thecatheter near the cardiac tissue that is to be ablated. The physiciandirects energy from the ablating element to ablate the tissue and form alesion.

In electrophysiological therapy, there is a growing need for ablatingelements capable of providing lesions in heart tissue having differentgeometries.

For example, it is believed the treatment of atrial fibrillationrequires the formation of long, thin lesions of different curvilinearshapes in heart tissue. Such long, thin lesion patterns require thedeployment within the heart of flexible ablating elements havingmultiple ablating regions. The formation of these lesions by ablationcan provide the same therapeutic benefits that the complex suturepatterns that the surgical maze procedure presently provides, butwithout invasive, open heart surgery.

As another example, it is believed that the treatment of atrial flutterand ventricular tachycardia requires the formation of relatively largeand deep lesions patterns in heart tissue. Merely providing "bigger"electrodes does not meet this need. Catheters carrying large electrodesare difficult to introduce into the heart and difficult to deploy inintimate contact with heart tissue. However, by distributing the largerablating mass required for these electrodes among separate, multipleelectrodes spaced apart along a flexible body, these difficulties can beovercome.

With larger and/or longer multiple electrode elements comes the demandfor more precise control of the ablating process. The delivery ofablating energy must be governed to avoid incidences of tissue damageand coagulum formation. The delivery of ablating energy must also becarefully controlled to assure the formation of uniform and continuouslesions, without hot spots and gaps forming in the ablated tissue.

SUMMARY OF THE INVENTION

A principal objective of the invention is to provide improved systemsand methodologies that control additive heating effects to formelongated straight or curvilinear lesion patterns in body tissue.

One aspect of the invention provides a device and associated method forcreating elongated lesion patterns in body tissue. The device and methoduse a support element that contacts a tissue area. The support elementcarries at least two non-contiguous energy emitting zones, which arelocated in a mutually spaced apart relationship along the contactedtissue area. In use, the zones are conditioned to simultaneously emitenergy to ablate tissue. The spacing between the zones along thecontacted tissue area determines the characteristic of the elongatedlesion patterns so formed.

When the zones are sufficiently spaced in close proximity to each other,the simultaneous transmission of energy from the zones in a unipolarmode (i.e., to an indifferent electrode) generates additive heatingeffects that create an elongated continuous lesion pattern in thecontacted tissue area. When the zones are not sufficiently spaced closeenough to each other, the simultaneous transmission of energy from thezones to an indifferent electrode do not generate additive heatingeffects. Instead, the simultaneous transmission of energy from the zonescreates an elongated segmented, or interrupted, lesion pattern in thecontacted tissue area.

In one embodiment, the spacing between the zones is equal to or lessthan about 3 times the smaller of the diameters of the first and secondzones. In this arrangement, the simultaneous transmission of energy fromthe zones to an indifferent electrode creates an elongated continuouslesion pattern in the contacted tissue area due to additive heatingeffects. Conversely, in another embodiment where the spacing between thezones is greater than about 5 times the smaller of the diameters of thefirst and second zones, the simultaneous transmission of energy from thezones to an indifferent electrode does not generate additive heatingeffects. Instead, the simultaneous transmission of energy from the zonescreates an elongated segmented, or interrupted, lesion pattern in thecontacted tissue area.

In another embodiment, the spacing between the zones along the contactedtissue area is equal to or less than about 2 times the longest of thelengths of the first and second zones. This mutually close spacingcreates, when the zones simultaneously transmit energy to an indifferentelectrode, an elongated continuous lesion pattern in the contactedtissue area due to additive heating effects. Conversely, in anotherembodiment where the spacing between the zones along the contactedtissue area is greater than about 3 times the longest of the lengths ofthe first and second zones, when the zones simultaneously transmitenergy to an indifferent electrode, an elongated segmented, orinterrupted, lesion pattern results.

Another aspect of the invention provides a device and associated methodfor creating elongated curvilinear lesion patterns in body tissue. Thedevice and method use a curved support element that contacts a tissuearea. At least two non-contiguous energy emitting zones are carried onthe curved support element mutually separated across the contactedtissue area.

In one embodiment, the zones are spaced across the contacted tissue areaby a distance that is greater than about 8 times the smaller of thediameters of the first and second zones. In this arrangement, thesimultaneously emission of energy forms an elongated lesion patternforms in the tissue area that follows the curved periphery contacted bythe support element, but does not span across the contacted tissue area.The curvilinear lesion pattern is continuous if the spacing between thezones along the support body is sufficient to create an additive heatingeffect. Otherwise, the curvilinear lesion pattern is segmented orinterrupted along its length.

In another embodiment, the zones are positioned along the support bodyhaving a radius of curvature that is greater than about 4 times thesmaller of the diameters of the first and second zones. In thisarrangement, the simultaneous emission of energy by the zones forms anelongated lesion pattern in the tissue area that follows the curvedperiphery contacted by the support element, but does not span across thecontacted tissue area. The curvilinear lesion pattern is continuous ifthe spacing between the zones along the support body is sufficient tocreate an additive heating effect. Otherwise, the curvilinear lesionpattern is segmented or interrupted along its length.

Other features and advantages of the inventions are set forth in thefollowing Description and Drawings, as well as in the appended Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a view of a probe that carries a flexible ablating elementhaving multiple temperature sensing elements;

FIG. 2 is an enlarged view of the handle of the probe shown in FIG. 1,with portions broken away and in section, showing the steering mechanismfor flexing the ablating element;

FIGS. 3 and 4 show the flexure of the ablating element against differenttissue surface contours;

FIG. 5 is a side view of a flexible ablating element comprising a rigidtip electrode element and a rigid body electrode segment;

FIG. 6 is a perspective view of a segmented flexible electrode element,in which each electrode segment comprises a wrapped wire coil;

FIGS. 7A/B are, respectively, side and side section views of differentwrapped wire coils comprising flexible electrode elements;

FIGS. 8A/B are, respectively, a side and side section view of multiplewrapped wire coils comprising a flexible electrode element;

FIG. 9 is a side view of a flexible ablating element comprising a rigidtip electrode element and a flexible body electrode segment;

FIG. 10 is a perspective view of a continuous flexible electrode elementcomprising a wrapped wire coil;

FIG. 11 is a perspective view of a continuous flexible electrode elementcomprising a wrapped ribbon;

FIGS. 12A/B are views of a flexible ablating element comprising awrapped wire coil including a movable sheath for changing the impedanceof the coil and the ablating surface area when in use;

FIGS. 13A/B are side views of, respectively, segmented electrodeelements and a continuous electrode element which have been masked onone side with an electrically and thermally insulating material;

FIGS. 14A/B are schematic views of electrically connecting electrodesegments to, respectively, single and multiple wires;

FIGS. 15A/B are side section views of forming flexible coil segmentsfrom the electrical conducting wires;

FIGS. 16A/B are views of various shaped multiple electrode structuresfor making lesions that span across diagonally and/or diametric spacedelectrode regions;

FIGS. 17A/18A are views of a generally circular multiple electrodestructure for making lesions that span across diagonally and/ordiametric spaced electrode regions;

FIGS. 17B/18B are views of a generally spiral multiple electrodestructure for making lesions that span across diagonally and/ordiametric spaced electrode regions;

FIGS. 19A/B/C are views of a generally hoop-shaped multiple electrodestructure for making lesions that span across diagonally and/ordiametric spaced electrode regions;

FIG. 20 is an end section view of an ablating electrode element carryingone temperature sensing element;

FIG. 21 is an end section view of an ablating electrode element carryingtwo temperature sensing elements;

FIG. 22 is an end section view of an ablating electrode element carryingthree temperature sensing elements;

FIG. 23 is a side section view of a flexible ablating element comprisingmultiple rigid electrode elements, showing one manner of mounting atleast one temperature sensing element beneath the electrode elements;

FIG. 24 is a side section view of a flexible ablating element comprisingmultiple rigid electrode elements, showing another manner of mounting atleast one temperature sensing element between adjacent electrodeelements;

FIG. 25 is a side section view of a flexible ablating element comprisingmultiple rigid ablating elements, showing another manner of mounting atleast one temperature sensing element on the electrode elements;

FIG. 26 is an enlarged top view of the mounting the temperature sensingelement on the rigid electrode shown in FIG. 26;

FIGS. 27 and 28 are side section views of the mounting of temperaturesensing elements on the ablating element shown in FIG. 5;

FIG. 29 is a view of a flexible ablating element comprising a continuouswrapped coil, showing one manner of mounting temperature sensingelements along the length of the coil;

FIG. 30 is a view of a flexible ablating element comprising a continuouswrapped coil, showing another manner of mounting temperature sensingelements along the length of the coil;

FIG. 31 is an enlarged view of the mounting of the temperature sensingelement on the coil electrode shown in FIG. 30;

FIG. 32 is a view of a flexible ablating element comprising a continuouswrapped ribbon, showing a manner of mounting temperature sensingelements along the length of the ribbon;

FIG. 33A is a top view of an elongated lesion pattern that is generallystraight and continuous, which non-contiguous energy emitting zonesform, when conditioned to simultaneous transmit energy to an indifferentelectrode, provided that they are spaced sufficiently close to eachother to generate additive heating effects;

FIG. 33B is a top view of an elongated lesion pattern that is generallystraight and segmented, which non-contiguous energy emitting zones formwhen they are not spaced sufficiently close to each other to generateadditive heating effects;

FIG. 34A is a top view of an elongated, curvilinear lesion pattern thatis continuous, which non-contiguous energy emitting zones create whenthey are sufficiently close to each other along the periphery of acurvilinear path generate additive heating effects between them whenthey simultaneously emit energy, but when they are otherwise positionedfar enough apart across from each other to not generate additive heatingeffects that span across the curvilinear path;

FIG. 34B is a top view of an elongated, curvilinear lesion pattern thatis segmented or interrupted, which non-contiguous energy emitting zonescreate when they are not sufficiently adjacent to each other eitheralong or across the periphery of a curvilinear path to generate additiveheating effects between them; and

FIG. 35 is a top view of a large lesion pattern that spans across acurvilinear path, which non-contiguous energy emitting zones create whenthey are sufficiently adjacent to each other to generate additiveheating effects across the periphery of the curvilinear path.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This Specification discloses multiple electrode structures that embodyaspects the invention. This Specification also discloses tissue ablationsystems and techniques using multiple temperature sensing elements thatembody other aspects of the invention. The illustrated and preferredembodiments discuss these structures, systems, and techniques in thecontext of catheter-based cardiac ablation. That is because thesestructures, systems, and techniques are well suited for use in the fieldof cardiac ablation.

Still, it should be appreciated that the invention is applicable for usein other tissue ablation applications. For example, the various aspectsof the invention have application in procedures for ablating tissue inthe prostrate, brain, gall bladder, uterus, and other regions of thebody, using systems that are not necessarily catheter-based.

I. Flexible Ablating Elements

FIG. 1 shows a flexible ablating element 10 for making lesions withinthe heart.

The element 10 is carried at the distal end of a catheter body 12 of anablating probe 14. The ablating probe 14 includes a handle 16 at theproximal end of the catheter body 12. The handle 16 and catheter body 12carry a steering mechanism 18 for selectively bending or flexing theablating element 10 in two opposite directions, as the arrows in FIG. 1show.

The steering mechanism 18 can vary. In the illustrated embodiment (seeFIG. 2), the steering mechanism 18 includes a rotating cam wheel 20 withan external steering lever 22 (see FIG. 1). As FIG. 2 shows, the camwheel 20 holds the proximal ends of right and left steering wires 24.The wires 24 pass through the catheter body 12 and connect to the leftand right sides of a resilient bendable wire or spring 26 (best shown inFIGS. 20 and 23) enclosed within a tube 28 inside the ablating element10.

Further details of this and other types of steering mechanisms for theablating element 10 are shown in Lundquist and Thompson U.S. Pat. No.5,254,088, which is incorporated into this Specification by reference.

As FIG. 1 shows, forward movement of the steering lever 22 flexes orcurves the ablating element 10 down. Rearward movement of the steeringlever 22 flexes or curves the ablating element 10 up.

Various access techniques can be used to introduce the probe 14 into thedesired region of the heart. For example, to enter the right atrium, thephysician can direct the probe 14 through a conventional vascularintroducer through the femoral vein. For entry into the left atrium, thephysician can direct the probe 14 through a conventional vascularintroducer retrograde through the aortic and mitral valves.

Alternatively, the physician can use the delivery system shown inpending U.S. application Ser. No. 08/033,641, filed Mar. 16, 1993, andentitled "Systems and Methods Using Guide Sheaths for Introducing,Deploying, and Stabilizing Cardiac Mapping and Ablation Probes."

The physician can verify intimate contact between the element 10 andheart tissue using conventional pacing and sensing techniques. Once thephysician establishes intimate contact with tissue in the desired heartregion, the physician applies ablating energy to the element 10. Thetype of ablating energy delivered to the element 10 can vary. In theillustrated and preferred embodiment, the element 10 emitselectromagnetic radio frequency energy.

The flexible ablating element 10 can be configured in various ways. Withthese different configurations, the flexible ablating element can formlesions of different characteristics, from long and thin to large anddeep in shape.

A. Segmented, Rigid Electrode Elements

FIGS. 3 and 4 show one implementation of a preferred type of flexibleablating element, designated 10(1). The element 10(1) includes multiple,generally rigid electrode elements 30 arranged in a spaced apart,segmented relationship upon a flexible body 32.

The flexible body 32 is made of a polymeric, electrically nonconductivematerial, like polyethylene or polyurethane. The body 32 carries withinit the resilient bendable wire or spring with attached steering wires(best shown in FIGS. 20 and 23), so it can be flexed to assume variouscurvilinear shapes.

The segmented electrodes 30 comprise solid rings of conductive material,like platinum. The electrode rings 30 are pressure fitted about the body32. The flexible portions of the body 32 between the rings 30 compriseelectrically nonconductive regions.

The body 32 can be flexed between the spaced apart electrodes 30 tobring the electrode 30 into intimate contact along a curvilinear surfaceof the heart wall, whether the heart surface curves outward (as FIG. 3shows) or curves inward (as FIG. 4 shows).

FIG. 5 shows an implementation of another preferred type of a flexibleablating element, of the same general style as element 10(1), designated10(2). Element 10(2) includes two generally rigid electrode elements 34and 36 arranged in a spaced apart relationship at the distal tip of aflexible body 38. The flexible body 38 is made of electricallyinsulating material, like polyurethane and PEBAX® plastic material. Thebody 38 carries one relatively large, rigid metal electrode 34 at itstip, which comprises a body of electrically conductive material, likeplatinum. The body 38 also carries another rigid electrode 36, whichcomprises a solid ring 36 of electrically conductive material, likeplatinum, pressure fitted about the body 38. As FIG. 5 shows, theablating element 10(2) can also include one or more conventional sensingring electrodes 40 proximally spaced from the ablating ring electrode36. The sensing ring electrodes 40 serve to sense electrical events inheart tissue to aid the physician in locating the appropriate ablationsite.

As shown in phantom lines in FIG. 5, the flexible body 38, when pressedagainst the endocardial surface targeted for ablation, bends to placethe sides of the rigid electrodes 34 and 36 in intimate contact againstthe particular contour of the surface. The flexible nature of theablating element 10(2) can be further augmented by the inclusion of theresilient bendable wire or spring 26 within it (best shown in FIG. 27).In this embodiment, the steering wires 24 connect to the left and rightsides of the bendable wire 26. The opposite ends of the steering wires24 connect to a steering mechanism of the type previously described andshown in FIG. 2. In this arrangement, the physician can use the steeringmechanism to remotely flex the electrodes 34 and 36 in the manner shownin FIG. 5.

Preferably, as FIG. 27 shows, the steering wires 24 are secured to thebendable wire 26 near its distal end, where the bendable wire 26 isitself secured to the tip electrode 34. Bending of the wire 26 therebydirectly translates into significant relative flexing of the distal endof the catheter body 38, which carries the electrodes 34 and 36.

Alternatively, the region between the electrodes 34 and 36 can be stiff,not flexible. In this arrangement, pressing the 34 and 36 against tissuebrings the tissue into conformance about the electrodes 34 and 36.

The generally rigid, segmented electrodes 30 in element 10(1) and 34/36in element 10(2) can be operated, at the physician's choice, either in aunipolar ablation mode or in a bipolar mode. In the unipolar mode,ablating energy is emitted between one or more the electrodes 30 (inelement 10(1)) or electrodes 34/36 (in element 10(2)) and an externalindifferent electrode. In the bipolar mode, ablating energy is emittedbetween two of the electrodes 30 (in element 10(1)) or the electrodes 34and 36 (in element 10(2)), requiring no external indifferent electrode.

B. Flexible Electrode Elements

FIG. 6 shows an implementation of another preferred style of a flexibleablating element, designated 10(3). The element 10(3), unlike elements10(1) and 10(2), includes generally flexible electrode elements 44carried on a likewise flexible body 42.

The flexible body 42 is made of a polymeric, electrically nonconductivematerial, like polyethylene or polyurethane, as the flexible body ofelements 10(1) and 10(2). The body 42 also preferably carries within itthe resilient bendable wire or spring 26 with attached steering wires 24(best shown in FIGS. 29 and 30), so it can be flexed to assumed variouscurvilinear shapes, as FIG. 6 shows.

The body 32 carries on its exterior surface an array of segmented,generally flexible electrodes 44 comprising spaced apart lengths ofclosely wound, spiral coils. The coil electrodes 44 are made ofelectrically conducting material, like copper alloy, platinum, orstainless steel. The electrically conducting material of the coilelectrode 44 can be further coated with platinum-iridium or gold toimprove its conduction properties and biocompatibility.

The coils 44 can be made of generally cylindrical wire, as the coil44(a) shown in FIGS. 7A/B. Alternatively, the wire forming the coils 44can be non-circular in cross section. The wire, for example, have apolygon or rectangular shape, as the coil 44(b) shown in FIGS. 7A/B. Thewire can also have a configuration in which adjacent turns of the coilnest together, as the coil 44(c) shown in FIGS. 7A/B. Coils 44(b) and44(c) in FIGS. 7A/B present a virtually planar tissue-contactingsurface, which emulates the tissue surface contact of the generallyrigid electrode 30 shown in FIGS. 3 and 4. However, unlike the electrode30, the coils 44(b) and 44(c), as well as the cylindrical coil 44(a),are each inherently flexible and thereby better able to conform to thesurface contour of the tissue.

In another alternative arrangement, each coil 44 can comprise multiple,counter wound layers of wire, as the coil 44(d) shown in FIGS. 8A/B.This enhances the energy emitting capacity of the coil 44(d), withoutsignificantly detracting from its inherent flexible nature. The multiplelayer coil 44(d) structure can also be formed by using a braided wirematerial (not shown).

An alternative arrangement (shown in FIG. 9) uses the generally rigidtip electrode 34 (like that in element 10(2), shown in FIG. 5) incombination with a generally flexible electrode segment 44 made of aclosely wound coil. Of course, the tip electrode 34, too, could comprisea generally flexible electrode structure made of a closely wound coil.It should be apparent by now that many combinations of rigid andflexible electrode structures can be used in creating a flexibleablating element.

Furthermore, the inherent flexible nature of a coiled electrodestructures 44 makes possible the constructure of a flexible ablatingelement (designated 10(4) in FIG. 10) comprising a continuous elongatedflexible electrode 46 carried by a flexible body 48. The continuousflexible electrode 46 comprises an elongated, closely wound, spiral coilof electrically conducting material, like copper alloy, platinum, orstainless steel, wrapped about the flexible body. For better adherence,an undercoating of nickel or titanium can be applied to the underlyingflexible body. The continuous coil electrode 46 can be arranged andconfigured in the same fashion as the segmented coil electrodes 44 shownin FIGS. 7A/B and 8A/B.

The continuous coil electrode 46 is flexible and flexes with theunderlying body 48, as FIG. 10 shows. It can be easily placed andmaintained in intimate contact against heart tissue. The continuousflexible coil structure shown in FIG. 10 therefore makes possible alonger, flexible ablating element.

In an alternative arrangement (shown in FIGS. 12A/B), the elongated coilelectrode 46 can include a sliding sheath 50 made of an electricallynonconducting material, like polyimide. A stylet (not shown) attached tothe sheath 50 extends through the associated catheter body 12 to asliding control lever carried on the probe handle 16 (also not shown).Moving the sheath 50 varies the impedance of the coil electrode 46. Italso changes the surface area of the element 10(4).

Further details of this embodiment can be found in copending U.S. patentapplication Ser. No. 08/137,576, filed Oct. 15, 1993, and entitled"Helically Wound Radio Frequency Emitting Electrodes for CreatingLesions in Body Tissue," which is incorporated into this Specificationby reference.

FIG. 11 shows another implementation of a generally flexible element,designated element 10(5). The element 10(5) comprises a ribbon 52 ofelectrically conductive material wrapped about a flexible body 54. Theribbon 52 forms a continuous, inherently flexible electrode element.

Alternatively, the flexible electrodes can be applied on the flexiblebody by coating the body with a conductive material, likeplatinum-iridium or gold, using conventional coating techniques or anion beam assisted deposition (IBAD) process. For better adherence, anundercoating of nickel or titanium can be applied. The electrode coatingcan be applied either as discrete, closely spaced segments (to create anelement like 10(3)) or in a single elongated section (to create anelement like 10(4) or 10(5)).

The flexible electrodes of elements 10(3) can be operated, at thephysician's choice, either in a unipolar ablation mode or in a bipolarmode.

C. Controlling Lesion Characteristics Usina Flexible Electrodes

The ablating elements 10(1) to 10(5), as described above, are infinitelyversatile in meeting diverse tissue ablation criteria.

For example, the ablating elements 10(1) and 10(3) to 10(5) can beconditioned to form different configurations of elongated (i.e.,generally long and thin) lesion patterns. These elongated lesionpatterns can be continuous and extend along a straight line (as lesionpattern 200 in FIG. 33A shows) or along a curve (as lesion pattern 204in FIG. 34A shows). Alternatively, these elongated lesion patterns canbe segmented, or interrupted, and extend along a straight line (aslesion pattern 202 in FIG. 33B shows) or along a curve (as lesionpattern 206 in FIG. 34B shows). Elongated lesion patterns can be used totreat, for example, atrial fibrillation.

Alternatively, the ablating elements 10(1) to 10(5) can be conditionedto form larger and deeper lesions in the heart, as lesion pattern 208 inFIG. 35 shows. These lesion large and deep lesion patterns can be usedto treat, for example, atrial flutter or ventricular tachycardia.

The characteristics of lesions formed by the ablating elements 10(1) to10(5) can be controlled in various ways. For example, lesioncharacteristics are controlled by employing one or more of the followingtechniques:

(i) selectively adjusting the size and spacing of energy emittingregions along the elements.

(ii) selectively masking the energy emitting regions on the elements tofocus ablating energy upon the targeting tissue.

(iii) selectively altering the electrical connections of wires conveyingablating energy to the energy emitting regions on the elements, tothereby affect the distribution of ablation energy.

(iv) selectively altering the shape of the flexible support body, tothereby affect the distribution and density of energy emitting regionson the elements.

(v) selectively controlling temperature conditions along the energyemitting regions of the elements.

These various techniques of controlling lesion characteristics will nowbe individually discussed in greater detail.

1. Size and Spacing of Energy Emitting Regions

The number of electrode segments that the elements 10(1), (2); (4); and(5) carry, and the spacing between them, can vary, according to theparticular objectives of the ablating procedure. Likewise, thedimensions of individual electrode segments and underlying body inelements 10(1) to 10(5) can also vary for the same reason. Thesestructural features influence the characteristics of the lesion patternsformed.

The continuous electrode structure of 10(4) is well suited for creatingcontinuous, elongated lesion patterns like the patterns 200 and 204shown in FIGS. 33A and 34A, when the entire electrode is conditioned toemit energy. The segmented electrode structures of elements 10(1); (3);and (5) are also well suited for creating continuous, elongated lesionpatterns like the pattern 200 shown in FIG. 33A, provided that theelectrode segments are adjacently spaced close enough together to createadditive heating effects when ablating energy is transmittedsimultaneously to the adjacent electrode segments. The same holds truewhen the continuous electrode structure 10(4) is conditioned to functionlike a segmented electrode structure by emitting energy from adjacentzones along its length, in which case the zones serve as electrodesegments. Stated another way, the segments comprise zones which emitenergy to tissue to obtain the desired therapeutic tissue heatingeffect.

The additive heating effects along a continuous electrode structure orbetween close, adjacent electrode segments intensify the desiredtherapeutic heating of tissue contacted by the segments. The additiveeffects heat the tissue at and between the adjacent electrode segmentsto higher temperatures than the electrode segments would otherwise heatthe tissue, if conditioned to individually emit energy to the tissue, orif spaced apart enough to prevent additive heating effects. The additiveheating effects occur when the electrode segments are operatedsimultaneously in a bipolar mode between electrode segments.Furthermore, the additive heating effects also arise when the continuouselectrode or electrode segments are operated simultaneously in aunipolar mode, transmitting energy to an indifferent electrode.

Conversely, when the energy emitting segments are not sufficientlyspaced close enough to each other to generate additive heating effects,the continuous electrode structure 10(4) and the segmented electrodestructures 10(1); (3); and (5) create elongated, segmented lesionpatterns like the pattern 202 shown in FIG. 33B.

More particularly, when the spacing between the segments is equal to orless than about 3 times the smaller of the diameters of the segments,the simultaneous emission of energy by the segments, either bipolarbetween the segments or unipolar to an indifferent electrode, creates anelongated continuous lesion pattern in the contacted tissue area due tothe additive heating effects. Conversely, when the spacing between thesegments is greater than about 5 times the smaller of the diameters ofthe segments, the simultaneous emission of energy by the segments,either bipolar between segments or unipolar to an indifferent electrode,does not generate additive heating effects. Instead, the simultaneousemission of energy by the zones creates an elongated segmented, orinterrupted, lesion pattern in the contacted tissue area.

Alternatively, when the spacing between the segments along the contactedtissue area is equal to or less than about 2 times the longest of thelengths of the segments the simultaneous application of energy by thesegments, either bipolar between segments or unipolar to an indifferentelectrode, also creates an elongated continuous lesion pattern in thecontacted tissue area due to additive heating effects. Conversely, whenthe spacing between the segments along the contacted tissue area isgreater than about 3 times the longest of the lengths of the segments,the simultaneous application of energy, either bipolar between segmentsor unipolar to an indifferent electrode, creates an elongated segmented,or interrupted, lesion pattern.

The continuous electrode structure 10(4) and the segmented electrodestructures 10(1); (3); and (5), when flexed can also create curvilinearlesion patterns like the patterns 204 and 206 shown in FIGS. 34A and34B. The peripheral shape of the lesion pattern can be controlled byflexing the body from straight to curvilinear. As already explained, thebody can be remotely steered to flex it into a desired shape, or it canpossess a preformed shape memory. In the latter situation, removing aconstraint (such as a sheath, not shown), enables the operator to changethe segment from straight to curvilinear.

To consistently form these curvilinear lesion patterns, additionalspacial relationships among the electrode segments must be observed. Theparticular nature of these relationships depends in large part upon thelength to diameter ratio of the individual electrode segments.

More particularly, when the length of each energy applying segment isequal to or less than about 5 times the diameter of the respectivesegment, the curvilinear path that support element takes should create adistance across the contacted tissue area that is greater than about 8times the smaller of the diameters of the first and second zones. Inthis arrangement, the simultaneously application of energy forms anelongated lesion pattern in the tissue area that follows the curvedperiphery contacted by the support element, but does not span across thecontacted tissue area. The curvilinear lesion pattern is continuous (asFIG. 34A shows) if the spacing between the segments along the supportelement is sufficient to create an additive heating effect between thesegments, as above described. Otherwise, the curvilinear lesion patternis segmented or interrupted along its length, as FIG. 34B shows.

When the length of each energy applying segment is greater than about 5times the diameter of the respective segment (which generally results inan elongated electrode structure like 10(4)), the curvilinear path thatsupport element takes should create a radius of curvature that isgreater than about 4 times the smallest the diameters segments. In thisarrangement, the simultaneous application of energy by the segments (bythe entire elongated electrode) forms an elongated lesion pattern in thetissue area that follows the curved periphery contacted by the supportelement, but does not span across the contacted tissue area. Again, thecurvilinear lesion pattern is continuous if the spacing between theenergy applying segments along the support body is sufficient to createan additive heating effect. Otherwise, the curvilinear lesion pattern issegmented or interrupted along its length.

Wider and deeper lesion patterns uniformly result by increasing thesurface area of the individual segments, due to the extra additiveeffects of tissue heating that the larger segments create. For thisreason, the larger surface areas of the electrode segments 34/36 inelement 10(2) are most advantageously used for forming large and deeplesion patterns, provided that both electrode segments 34/36 areconditioned to emit ablating energy simultaneously.

However, with all elements 10(1) to 10(5), ablating energy can beselectively applied individually to just one or a selected group ofelectrode segments, when desired, to further vary the size andcharacteristics of the lesion pattern.

Taking the above considerations into account, it has been found thatadjacent electrode segments having lengths of less than about 2 mm donot consistently form the desired continuous lesion patterns. Usingrigid electrode segments, the length of the each electrode segment canvary from about 2 mm to about 10 mm. Using multiple rigid electrodesegments longer than about 10 mm each adversely effects the overallflexibility of the element 10(1).

However, when flexible electrode segments are used, electrode segmentslonger that about 10 mm in length can be used. Flexible electrodesegments can be as long as 50 mm. If desired, the flexible electrodestructure can extend uninterrupted along the entire length of the body,thereby forming the continuous elongated electrode structure 46 ofelement 10(4).

In the electrode structures of elements 10(1) to 10(5), the diameter ofthe electrode segments and underlying flexible body can vary from about4 french to about 10 french. When flexible electrode segments are used(as in elements 10(3) to 10(5)), the diameter of the body and electrodesegments can be less than when more rigid electrode segments are used(as in element 10(1)). Using rigid electrodes, the minimum diameter isabout 1.35 mm, whereas flexible electrodes can be made as small as about1.0 mm in diameter.

In a representative segmented electrode structure using rigid electrodesegments, the flexible body is about 1.35 mm in diameter. The bodycarries electrode segments each having a length of 3 mm. When eightelectrode segments are present and simultaneously activated with 100watts of radio frequency energy for about 60 seconds, the lesion patternis long and thin, measuring about 5 cm in length and about 5 mm inwidth. The depth of the lesion pattern is about 3 mm, which is more thanadequate to create the required transmural lesion (the atrial wallthickness is generally less than 3 mm).

In a representative segmented electrode structure using flexibleelectrode segments, the coil electrode 56 is about 1.3 mm in diameter,but could be made as small as 1.0 mm in diameter and as large as 3.3 mmin diameter. In this arrangement, the coil electrode 56 is about 5 cm intotal length. When activated with 80 watts of radio frequency energy for60 seconds, the coil electrode 56 forms a contiguous lesion pattern thatis about 3 mm in width, about 5 cm in length, and about 1.5 mm in depth.

Regarding the ablating element 10(2), the tip electrode 34 can range inlength from about 4 mm to about 10 mm. The electrode segment 36 can varyin length from about 2 mm to about 10 mm (or more, if it is a flexibleelongated electrode, as FIG. 9 shows). The diameter of the electrodes 34and 36, and thus the flexible body 38 itself, can vary from about 4french to about 10 french.

In element 10(2), the distance between the two electrodes 34 and 36 canalso vary, depending upon the degree of flexibility and the size of thelesion pattern required. In a representative embodiment, the electrodesegment 36 is spaced from the tip electrode 34 by about 2.5 mm to about5 mm. Thus, the effective ablating length presented by the combinedelectrodes 34 and 36 can vary from about 8.5 mm to about 25 mm.Preferably, the effective ablating length presented is about 12 mm.

2. Focusing Ablating Energy

As shown in FIGS. 13A/B, a side of one or more electrode segments ofelements 10(1), (2), and (3) (generally designated E_(SEG) in FIG. 13A),or a side of at least a portion of the continuous elongated electrode ofelement 10(4), and 10(5) (generally designated E_(CON) in FIG. 13B), canbe covered with a coating 56 of an electrically and thermally insulatingmaterial. This coating 56 can be applied, for example, by brushing on aUV-type adhesive or by dipping in polytetrafluoroethylene (PTFE)material.

The coating 56 masks the side of the electrode E_(SEG) and E_(CON) that,in use, is exposed to the blood pool. The coating 56 thereby preventsthe transmission of ablating energy directly into the blood pool.Instead, the coating 56 directs the applied ablating energy directlytoward and into the tissue.

The focused application of ablating energy that the coating 56 provideshelps to control the characteristics of the lesion. The coating 56 alsominimizes the convective cooling effects of the blood pool upon theelectrode E_(SEG) and E_(CON) while ablating energy is being applied,thereby further enhancing the efficiency of the lesion formationprocess.

3. Uniformly Distributing Ablating Energy

As FIG. 14A shows, the segmented electrodes E_(SEG) are electricallycoupled to individual wires 58, one serving each electrode segment, toconduct ablating energy to them. As FIG. 15A shows, in the case of asegmented coil electrode, the end of the connecting wire 50 itself canbe wrapped about the flexible body to form a flexible coil segment 44.

In the case of a continuous elongated electrode structure (like coilelectrode 46 of element 10(4)), wires 58 are preferable electricallycoupled to the coil 46 at equally spaced intervals along its length.This reduces the impedance of the coil along its length. As alreadyexplained, and as FIGS. 12A/B show, the elongated coil electrode canalso include a sliding sheath 50 to vary the impedance.

In an alternative embodiment, shown in FIG. 14B, there are two spacedapart wires 58(1) and 58(2) electrically coupled to each segmentedelectrode E_(SEG). In this arrangement, power is delivered in parallelto each segmented electrode E_(SEG). This decreases the effect ofvoltage gradients within each segmented electrode E_(SEG), which, inturn, improves the uniformity of current density delivered by theelectrode E_(SEG). The spacing between the multiple wires serving eachelectrode segment E_(SEG) can be selected to achieve the uniformity ofcurrent density desired.

As FIG. 15B shows, each flexible coil segment 44 can also comprise twoor more individual wires 58(1) and 58(2) wrapped at their ends, whichtogether form the coil segment. The multiple wires can be wrappedsequentially or in a staggered arrangement to form the coil segment.Similarly, an elongated flexible electrode can be formed by individuallengths of wire wrapped about the body, either sequentially or in astaggered pattern.

4. Distribution and Density of Energy Applying Segments

The flexible ablating elements 10(1) and 10(3) to 10(5) can also be usedto form larger and deeper lesion patterns by specially shaping thesupport body to increase the density of electrodes per given tissuearea. Structures suited for creating larger lesion patterns result whenthe flexible body is generally bent back upon itself to positionelectrode regions either diagonally close to each other (as structure 60in FIG. 16A shows) or both diagonally close and diametrically facingeach other (as structure 62 in FIG. 16B shows). The electrode regionscan be either energy emitting portions of a continuous flexibleelectrode E_(CON), as in structure 60 in FIG. 16A, or energy emittingsegments E_(SEG) of a segmented electrode structure, as in structure 62in FIG. 16B.

This close diagonal spacing and/or close diametric facing of electrodesthat the structures 60 and 62 provide, coupled with the simultaneousemission of ablating energy by the electrodes on the structures 60 and62, significantly concentrates the distribution of ablating energy.These specially shaped electrode structures 60 and 62 provide anadditive heating effect that causes lesions to span across electrodesthat are diagonally close and/or diametrically facing. The spanninglesions create large and deep lesion patterns in the tissue region thatthe structures 60 and 62 contact.

The structures 60 and 62 best provide these larger and deeper lesionpatterns when they maintain a prescribed relationship among theelectrode regions that takes into account the geometry of the structure,the dimension of the structure, and the dimension of the electroderegions it carries.

More particularly, when the length of each energy emitting region orzone is greater than about 5 times the diameter of the respective regionor zone (as would be the case in the continuous electrode E_(CON) inFIG. 16A, or with a segmented electrode having large electrodesegments), the support structure should be bent back upon itself tomaintain a minimum radius of curvature (designated R_(D) in FIG. 16A)that does not exceed about 3.5 times the diameter of the smallestelectrode area (designated E_(D) in FIG. 16A). The support structure canbe shaped as a hook (as structure 60 in FIG. 16A) or as a circle (asstructure 62 in FIG. 16B) to present this minimum radius of curvature.

When the support structure establishes and maintains this relationship,the emission of ablating energy by the electrode E_(CON) along itslength will create a lesion that spans across the interior of thestructure 60 or 62, between the diagonal and facing electrode regions,due to additive heating effects. A large and deep lesion pattern likethe pattern 208 shown in FIG. 35 results, which occupies essentially allof the interior region enclosed by the structure 60 or 62. Foruniformity of lesion generation, R_(D) should preferably not exceedabout 2.5 times E_(D). Most preferably, R_(D) is less than about 1.5times E_(D).

Conversely, as described earlier, with energy emitting segments of thissize, if the curvilinear path that support element takes creates aradius of curvature R_(D) that is greater than about 4 times thesmallest the diameters segments, the simultaneous emission of energy bythe segments forms an elongated lesion pattern in the tissue area thatfollows the curved periphery contacted by the support element, but doesnot span across the contacted tissue area (like the lesion patterns 204and 206 shown in FIGS. 34A and 34B). The curvilinear lesion pattern iscontinuous, as shown in FIG. 34A, if the spacing between the energyemitting segments along the support body is sufficient close to createan additive heating effect between the segments, as would be the casefor a continuous electrode or closely spaced large segmented electrodes.Otherwise, the curvilinear lesion pattern is segmented or interruptedalong its length, as in FIG. 34B.

When the length of each energy applying region or zone is less than orequal to about 5 times the diameter of the respective region or zone (aswould be the case of an array of smaller segmented electrodes E_(SEG),like elements 10(1) and 10(3) and as shown in FIG. 16B), the supportstructure should be bent back upon itself so that the longest distancebetween facing electrode pairs diagonally or diametrically spaced toprovide an additive heat effect (designated S_(D) in FIG. 16B) does notexceed about 7 times the diameter of the smallest electrode segment(also designated E_(D) in FIG. 16B). In isoradial circular or hookshaped configurations, the longest distance S_(D) will occur betweendiametrically facing electrode segments (as FIG. 16B shows). When facingelectrode segments, subject to the above constraints, emit ablatingenergy simultaneously, a lesion uniformly spanning the space betweenthem will result due to additive heating effects. A large deep lesionuniformly occupying the region enclosed by the structure will be formed,as FIG. 35 shows.

For uniformity of lesion generation, S_(D) should be also preferably nogreater than about 5 times, and most preferably no greater than 3 times,E_(D). Conversely, if S_(D) exceeds about 8 times E_(D), a long and thinlesion pattern results, which follows the periphery of the structure,but does not uniformly span across the interior of the structure 60between diagonal or facing electrode regions. The curvilinear lesionpattern is continuous, as shown in FIG. 34A, if the spacing between theenergy applying segments along the support body is sufficient close tocreate an additive heating effect between the segments, as would be thecase for a continuous electrode or closely spaced large segmentedelectrodes. Otherwise, the curvilinear lesion pattern is segmented orinterrupted along its length, as in FIG. 34B.

Preferably, to further assure uniformity of lesion generation whensegmented electrodes are used, the S_(D) of the support structure 62should not exceed about 4 times the length of the longest facing segment(designated E_(L) in FIG. 16B). Most preferably, in a segmentedelectrode structure for creating large deep lesions, S_(D) should beless than about 3 times E_(L). This criterion holds true when the lengthis not substantially larger than the diameter. When the length is morethan about 5-fold larger than the diameter, the ablating element issimilar to a continuous electrode and the determining criterion for thelesion structure is the diameter of the ablation structure.

A large lesion can be created by placing in parallel facing relationship6 mm apart, two energy applying segments that are each 8 F in diameterand 3 mm in length, and applying RF energy simultaneously to bothsegments. When the application of energy by both segments is controlledto maintain temperatures at the segments of 80° C. for two minutes, thelesion width is about 12 mm, the lesion length is about 4 mm, and thelesion depth is about 7 mm.

Structures like those shown in FIGS. 16A and B that meet the abovecriteria can be variously constructed, depending upon the particularablation objectives desired. They can be in the shape of a doubled back,open circular structure like a hook (as structure 60 generallyrepresents), or a closed or concentric spiral structure (as structure 62generally represents).

As a further example, a preshaped circular structure 64 like FIGS. 17Aand 18A show can be used for creating lesion patterns for treatingatrial fibrillation. The structure 64 can extend axially from the distalend of the catheter body 12, as FIG. 17A shows. Alternatively, thestructure 64 can extend generally perpendicular to the distal end of thecatheter body, as FIG. 18A shows. The structure 64 can either carryrigid or flexible electrode segments 66 (as FIGS. 17A and 18A show), or,alternatively, the structure 64 can carry a continuous flexibleelectrode along its length.

As another example, a preshaped spiral structure 68 like FIGS. 17B and18B show can be used to form large lesion patterns for treatingventricular tachycardia. The structure 68 can extend axially from thedistal end of the catheter body 12, as FIG. 17B shows. Alternatively,the structure 68 can extend generally perpendicular to the distal end ofthe catheter body, as FIG. 18B shows. The structure 68 can either carryflexible electrode segments 70 (as FIGS. 17B and 18B show), or,alternatively, the structure 64 can carry a continuous flexibleelectrode along its length. The longest distance between the facingelectrodes throughout the spiral determines whether the lesion will spanthe regions between electrodes when they are simultaneously suppliedwith energy, following the criterion established above. If the abovecriterion is met, then the resulting lesion will be large and deep.

Further details of the spiral structure 68 are described in copendingpatent application Ser. No. 08/138,452, filed Oct. 14, 1993, andentitled "Systems and Methods for Locating and Ablating AccessoryPathways in the Heart," which is incorporated herein by reference.

As yet another example, a preshaped hoop structure 72 like FIGS. 19A/B/Cshow can be used to create lesion patterns useful in treating atrialfibrillation. The hoop structure 72 extends generally perpendicular fromthe distal end of the catheter body 12. As shown in FIG. 19A, the hoopstructure 72 can carry a continuous flexible electrode 74.Alternatively, the structure 72 can carry segmented flexible electrodes76, as FIG. 19B shows. Still alternatively, the structure 72 can carryrigid electrode segments 78.

5. Temperature Control at Multiple Energy Emitting Regions

In the illustrated and preferred embodiments, each flexible ablatingelement 10(1) to 10(5) carries at least one and, preferably, at leasttwo, temperature sensing element 80. The multiple temperature sensingelements 80 measure temperatures along the length of the element 10.

(i) Temperature Sensing with Rigid Electrode Elements

In the segmented element 10(1) (see FIGS. 3 and 4), each electrodesegment 30 preferably carries at least one temperature sensing element80. In this configuration, the sensing elements 80 are preferablylocated in an aligned relationship along one side of each segmentedelectrode 30, as FIGS. 3 and 4 show.

The body 32 preferably carries a fluoroscopic marker (like the stripe 82shown in FIGS. 3 and 4) for orientation purposes. The stripe 82 can bemade of a material, like tungsten or barium sulfate, which is extrudedinto the tubing 12. The extruded stripe can be fully enclosed by thetubing or it can be extruded on the outer diameter of the tubing makingit visible to the eye. FIG. 5 shows the marker in the wall of the tubing12. An alternative embodiment can be a fluoro-opaque wire like platinumor gold which can be extruded into the tubing wall. Yet anotherembodiment is to affix a marker in the inner diameter of the tubingduring manufacturing.

The sensing elements 80 can be on the same side as the fluoroscopicmarker 82 (as FIGS. 3 and 4 show), or on the opposite side, as long asthe physician is aware of the relative position of them. Aided by themarker 82, the physician orients the element 10(1) so that thetemperature sensing elements 80 contact the targeted tissue.

Alternatively, or in combination with the fluoroscopic marker 82, thesensing elements 80 can be consistently located on the inside or outsidesurface of element 10(1) when flexed in a given direction, up or down.For example, as FIG. 3 shows, when the element 10(1) is flexed to thedown, the sensing elements 80 are exposed on the inside surface of theelement 10(1). As FIG. 4 shows, when the element 10(1) flexed to theupward, the sensing elements 80 are exposed on the outside surface ofthe element 10 (1).

Each electrode segment 30 can carry more than a single temperaturesensing element 80. As FIGS. 20 to 22 show, each electrode segment 30can carry one, two, three, or more circumferentially spaced aparttemperature sensing elements 80. The presence of multiple temperaturesensing elements 80 on a single electrode segment 30 gives the physiciangreater latitude in positioning the ablating element 10(1), while stillproviding temperature monitoring.

As FIG. 20 shows, a mask coating 56, as above described, can also beapplied to the side of the single sensor-segmented electrode 30 oppositeto the temperature sensing element 80, which, in use, is exposed to theblood pool. As FIG. 21 shows, the mask coating 56 lies between the twosensors 80 on the bidirectional segmented electrode 30. The mask coating56 minimizes the convective cooling effects of the blood pool upon theregions of the electrode segment 80 that are exposed to it. Thetemperature condition sensed by the element 80 facing tissue is therebymore accurate. When more than two temperature sensors 80 are used on agiven electrode segment 30, masking becomes less advisable, as itreduces the effective surface of the electrode segment 30 available fortissue contact and ablation.

The temperature sensing elements 80 can comprise thermistors orthermocouples. When using thermocouples as the sensing elements 80, areference or cold junction thermocouple must be employed, which isexposed to a known temperature condition. The reference thermocouple canbe placed within the temperature processing element itself.Alternatively, the reference thermocouple can be placed within thehandle 18 of the catheter probe 14.

Further details regarding the use of thermocouples can be found in apublication available from Omega, entitled Temperature, pages T-7 toT-18. Furthermore, details of the use of multiple thermocouples astemperature sensing elements 80 in tissue ablation can be found incopending patent application Ser. No. 08/439,624, filed on the same dateas this application, entitled "Systems and Methods for ControllingTissue Ablation Using Multiple Temperature Sensing Elements."

The sensing element or elements 80 can be attached on or near thesegmented electrodes 30 in various way.

For example, as FIG. 23 shows for the element 10(1), each sensingelement 80 is sandwiched between the exterior of the flexible body 32and the underside of the associated rigid electrode segment 30. In theillustrated embodiment, the sensing elements 80 comprise thermistors.The body 32 is flexible enough to fit the sensing element 80 beneath theelectrode segment 30. The plastic memory of the body 32 maintainssufficient pressure against the temperature sensing element 80 toestablish good thermal conductive contact between it and the electrodesegment 30.

In an alternative embodiment (as FIG. 24 shows), the temperature sensingelement 80 is located between adjacent electrode segments 30. In thisarrangement, each sensing element 80 is threaded through the flexiblebody 32 between adjacent electrode segments 30. In the illustratedembodiment, the temperature sensing elements 80 comprise thermocouples.When the sensing element 80 comprises a thermocouple, an epoxy material46, such as Master Bond Polymer System EP32HT (Master Bond Inc.,Hackensack, N.J.), encapsulates the thermocouple junction 84, securingit to the flexible body 32. Alternatively, the thermocouple junction 84can be coated in a thin layer of polytetrafluoroethylene (PTFE)material. When used in thicknesses of less than about 0.002 inch, thesematerials have the sufficient insulating properties to electricallyinsulate the thermocouple junction 84 from the associated electrodesegment 30, while providing sufficient thermally conducting propertiesto establish thermal conductive contact with electrode segment 30. Theuse of such materials typically will not be necessary when thermistorsare used, because conventional thermistors are already encapsulated inan electrically insulating and thermally conducting material.

In another alternative embodiment (as FIGS. 25 and 26 show), thetemperature sensing element 80 physically projects through an opening 86in each electrode segment 30. As in the embodiment shown in FIG. 24, thesensing elements 80 comprise thermocouples, and a thermally conductingand electrically insulating epoxy material encapsulates the thermocouplejunction 84, securing it within the opening 86.

It should be appreciated that some sensing elements 80 can be carried bythe electrode segments 30, while other sensing elements 80 can becarried between the element segments 30. Many combinations of sensingelement locations are possible, depending upon particular requirementsof the ablating procedure.

In the element 10(2) (see FIG. 27), each electrode segment 34 and 36carries at least one temperature sensing element 80. In the illustratedembodiment, the sensing element 80 comprises a thermistor.

The tip electrode segment 34 carries a temperature sensing element 80within a cavity 88 drilled along its axis. The body electrode segment 36also carries at least one temperature sensing element 80, which issandwiched beneath the electrode segment 36 and the flexible body 38, inthe manner previously described and shown in FIG. 23. The sensingelement 80 in the electrode segment 36 can be alternatively secured inthe manners previously described and shown in FIGS. 24 and 25.Alternatively, as earlier described, the side of the electrode segment36 opposite to the single sensing temperature element 80 can carryingthe mask coating 56.

As shown in FIG. 28, either or both electrodes 34 and 36 of element10(2) can carry more than one temperature sensing element 80. In thisarrangement, the tip electrode 34 carries additional temperature sensingelements 80 in side cavities 90 that extend at angles radially from theaxis of the electrode 34. The body electrode segment 36 carriesadditional sensing elements 80 in the manner shown in FIGS. 21 and 22.

As the diameter of the electrodes 34 and 36 increases, the use ofmultiple temperature sensing elements 80 becomes more preferred. Themultiple sensing elements 80 are circumferentially spaced to assure thatat least one element 80 is in thermal conductive contact with the sametissue area as the associated electrode 34 or 36.

(ii) Temperature sensing with Flexible Electrode Elements

In the flexible electrode elements 10(3) and 10(4) (earlier shown inFIGS. 6 and 10), the multiple temperature sensing elements 80 arepreferably located at or near the electrical connection points betweenthe wires 58 and the coil electrode segments 44 or continuous coilelectrode 46, as FIGS. 29 and 30 best show. This location for thetemperature sensing elements 80 is preferred because higher temperaturesare typically encountered at these connection points along the coilelectrode 44 or 46.

As FIG. 29 shows, the sensing elements 80 can be secured to the insidesurface of the coil electrode 44 or 46. Alternatively, the sensingelements 80 can be sandwiched between the inside surface of theelectrode 44 or 46 and an underlying flexible body, as FIGS. 15A/B show.In FIGS. 15A/B and 29, the sensing elements 80 comprise thermistors.

Alternatively, as FIGS. 30 and 31 show, the sensing elements 80 can bethreaded up through the windings in the coil electrode 44 or 46 to layupon its exterior surface. In the illustrated embodiment, the sensingelements 80 comprise thermocouples, and the thermocouple junction 84 isencapsulated in on an epoxy or PTFE coating, as previously described.

When the elongated electrode 46 includes a sliding sheath 50 see FIGS.12A/B), the movable sheath 50 carries, in addition to the temperaturesensing elements 80 spaced along the length of the coil electrode 56,another temperature sensing element 80 at its distal end.

In the case of flexible electrode element 10(5) (earlier shown in FIG.11), the sensing elements 80 are sandwich ribbon 52 and wrapped ribbon52 and the underlying flexible body 54, as FIG. 32 shows. In theillustrated embodiment, the sensing elements 80 comprise thermocoupleshaving junctions 84 encapsulated in an electrically insulating andthermally conducting coating.

The various shaped electrode structures 64, 68, and 72 (see FIGS. 17A/B;18A/B; and 19A/B/C, respectively), can also carry multiple temperaturesensing elements 80 secured at spaced intervals along the shapedstructure, as these Figures show.

An external temperature processing element (not shown) receives andanalyses the signals from the multiple temperature sensing elements 80in prescribed ways to govern the application of ablating energy to theflexible ablating element 10. The ablating energy is applied to maintaingenerally uniform temperature conditions along the length of theelement.

When the element 10 carries segmented electrode structures, each havingmore than one sensing element 80, the controller selects the sensingelement 80 having the most intimate contact with tissue by selectingamong the sensed temperatures the highest sensed temperature. Thetemperature sensing element 80 providing the highest sensed temperaturefor a given electrode segment 30 is the one in most intimate contactwith heart tissue. The lower sensed temperatures of the other sensingelements 80 on the given electrode segment 30 indicate that the othersensing elements 80 are not in such intimate contact, and are insteadexposed to convective cooling in the blood pool.

Further details of the use of temperature sensing in tissue ablation canbe found in copending patent application Ser. No. 08/037,740, filed Mar.3, 1993, and entitled "Electrode and Associated Systems Using ThermallyInsulated Temperature Sensing Elements." Also, further details of theuse of multiple temperature sensing elements in tissue ablation can befound in copending patent application Ser. No. 08/439,624, filed on thesame date as this application, entitled "Systems and Methods forControlling Tissue Ablation Using Multiple Temperature SensingElements."

Various features of the invention are set forth in the following claims.

We claim:
 1. A device for ablating body tissue in a body defining anexterior, comprisinga support element to contact a tissue area, anindifferent electrode in spaced relation to the support element andadapted to be located on the exterior of the body, at least threenon-contiguous longitudinally spaced electrodes on the support elementmutually spaced apart along the support element, the mutual spacingbetween the electrodes being such that, when the electrodessimultaneously transmit energy through a contacted area to theindifferent electrode, a continuous lesion pattern is formed in thecontacted tissue area that spans between the at least three electrodes,and an energy source, operably connected to the at least threeelectrodes, adapted to simultaneously transmit energy to each of the atleast three electrodes such that each of the electrodes transmit energythrough the contacted area to the indifferent electrode.
 2. A deviceaccording to claim 1wherein the support element includes a generallystraight region, and wherein the electrodes are on the generallystraight region.
 3. A device according to claim 1wherein the supportelement includes a curved region, and wherein the electrodes are on thecurved region.
 4. A device according to claim 1wherein at least one ofthe electrodes comprises metallic material attached about the supportelement.
 5. A device according to claim 1wherein at least one of theelectrodes comprises wire helically wrapped about the support element.6. A device according to claim 1wherein the support element is flexibleand includes means for flexing the element.
 7. A device according toclaim 1, wherein each of the electrodes comprises a helical electrodeincluding a plurality of windings extending around the support element.8. A method for ablating body tissue in a body defining an exterior,comprising the steps ofpositioning at least three non-contiguouslongitudinally spaced energy emitting zones in a mutually closely spacedapart relationship in contact with a tissue area, positioning anindifferent electrode on the exterior of the body, and energizing the atleast three zones to simultaneously transmit energy through thecontacted tissue area to the indifferent electrode to create, due to theclose spacing of the zones, a continuous lesion pattern in the contactedtissue area spanning between the at least three zones.
 9. A device forablating body tissue in a body defining an exterior, comprisinga supportelement to contact a tissue area, an indifferent electrode in spacedrelation to the support element and adapted to be located on theexterior of the body, at least two non-contiguous longitudinally spacedelectrodes on the support element mutually spaced apart along thesupport element, the mutual spacing between the electrodes being suchthat, when the electrodes simultaneously transmit energy through acontacted area to the indifferent electrode, a continuous lesion patternis formed in the contacted tissue area that spans between the at leasttwo electrodes, and an energy source, operably connected to the at leasttwo electrodes, adapted to simultaneously transmit energy to each of theat least two electrodes such that each of the electrodes transmit energythrough the contacted area to the indifferent electrode.
 10. A device asclaimed in claim 9, wherein the support element defines an outer surfaceand each of the electrodes extends continuously and completely aroundthe outer surface the support element.